A. Field of the Invention
The present invention relates to a device for the virtual display of an image. More specifically the present invention relates to a device for the virtual display of moving images such as video, motion pictures and the like.
B. Discussion of the Prior Art
Devices are known for the production of a virtual image outside of such devices using an illuminated real object which is included fixedly or rotatably within the devices. In one such device, the virtual image is produced outside the housing by means of a fresnel lens which is arranged in the housing opening. The object can either be arranged lying directly opposite the fresnel lens inside the housing or staggered with respect to the fresnel lens, with the object then being depicted onto the fresnel lens by a suitable mirror arrangement. Such a three-dimensional image device is disclosed in European Patent No. EP-B1-0 410 968 by Raul Orlandi.
While suited for their intended purpose, a disadvantage of devices of this type is that only illuminated real objects can be depicted, which is complicated in practice and greatly restricts the use of this image device to objects which can be maintained in the housing. Whereas flat objects can be depicted with such a device with relatively no difficulty, three-dimensional distortions occur in the depicting of objects with greater three-dimensional depth. In addition, the observation of the image is substantially limited to a particular viewing axis, which is determined by the foci of the fresnel lens. In other words, this known device suffers from a very tight viewing angle. To increase the viewing angle, a 3 to 1 size ratio is desired between the object and the lens. Thus, the object is generally 3 times smaller than the lens to increase the viewing angle.
The disadvantages set out above also apply to an alternative embodiment known in which the depiction of the real object takes place by means of a concave mirror arranged in the path of light rays and a partially translucent mirror, instead of with a fresnel lens. Finally, it is disadvantageous that an observer always has to look into the fresnel lens or into the concave mirror in order to observe the object, which is very disturbing due to the enlargement of the mirror image of the observer.
An object of the present invention consists of largely eliminating the above-mentioned disadvantages and providing a virtual image device in accordance with the present invention in which the range of applications for the device is expanded and which ensures an undistorted image reproduction of the subject which is to be depicted, with a greater viewing angle than hitherto.
These disadvantages are solved by the features of the virtual image device of the present invention comprising a housing with an observation opening in a wall of the housing, an image source for the virtual image to be depicted, and imaging optics arranged in the housing for projecting the image onto a fresnel lens, located in the observation opening. The imaging optics have a part-spherical mirror arranged in the path of light rays between the image source and the fresnel lens. The image source, which may be a real object, is preferably generated by a two-dimensional (2-D) projection device.
The invention overcomes the problems disclosed above by featuring an improved imaging system based on the combination of a fresnel lens and a part-spherical mirror. The part spherical mirror is preferably a concave mirror, but a convex mirror is acceptable. In addition, as a substitute for the real object disclosed in the prior art, the virtual image is generated by an image projection device that creates a 2-D image at the image source.
According to the invention, through the combination of a concave mirror and fresnel lens, the viewing angle can be increased without a costly (oversized) fresnel lens being used as in the prior art, which is desirably 3 times greater than the image which is to be depicted, for the enlargement of the viewing angle.
Through the use of a 2-D projection device to produce an image at the image source, rather than using a real object, distortions are virtually eliminated. A further advantage of the use of a 2-D projection device to produce an image rather than using a real object is that complex animation can also be depicted without difficulty, for example, several objects can be displayed moving simultaneously. Another feature of the 2-D projection device according to the invention is that a re-adjustment of the device is not required when real objects are exchanged as in the prior art. Furthermore, an opening in the housing of the device necessary for exchanging real objects is not required. Hence, completely new fields of applications become possible for the device according to the present invention, in particular for advertising, because images which are to be projected can be played back in a simple manner by video for example, preferably controlled by computer.
A variety of imaging means come into consideration for the two-dimensional projection device, such as for example a slide or film projector or a video or laser image production device. The video image production device preferably comprises a video projector, a video monitor, a television set, an LCD screen or the like.